1372 



VEIN. 



masses of white fibrous tissue are obliterated. 

 When treated with this reagent the fibres of 

 this coat lose their wavy character to a cer- 

 tain extent, and present intersecting undula- 

 tions. (Fig. 857. a.) When the internal coat 

 is seen in transverse section, it presents a 

 granular, indistinct appearance, without fibres 

 of any determinate direction : in some places 

 it presents lines of a crumpled or corrugated as- 

 pect. In j%. 858. a, this may be seen, as also 

 its distinctness from the next coat, from which 

 it is separated at one part by a slight interval. 



This coat appears to exist in all the veins, 

 and in the smaller ones, and larger capillaries 

 when treated with acetic acid, as hereafter to 

 be described, its presence would seem to be 

 indicated by the internal longitudinal nuclei, 

 which are then displayed. 



Middle coat, of intermixed circular and lon- 

 gitudinal fibres. This tunic occupies about 

 one-fourth of the entire thickness of the wall 

 of a vein. Its internal boundary is sharp and 

 distinct, where this coat is in contact with the 

 internal, but the outer boundary, where it gra- 

 dually merges into the external, is indefinite, 

 and indeed artificial. 



In fig. 856. the middle coat is represented 

 at b, and is composed of intermixed fibres of 

 longitudinal and transverse yellow elastic 

 tissue embedded in a nidus of white fibre. As 

 this figure represents a longitudinal section, 

 the transverse fibres of the yellow element 



Fig. 857. 



Longitudinal vertical Section of Wall of Subclavian 

 Vein of Ox, treated with Acetic Acid. 



a, internal coat ; b, middle coat ; c, part of external 

 coat. (Magnified 200 diameters.) 



are seen cut across, and appear as small discs : 

 on the other hand, the longitudinal fibres 

 with which they are mingled, are seen in pro- 

 file, as interlacing and parallel rods : the 



former gradually diminish, and the latter, in 

 the same proportion, increase, as viewed fur- 

 ther and further from the inner surface ; and 

 that point where the discs entirely disappear 

 and the longitudinal fibres alone remain may 

 be considered as the external limit of the 

 middle coat. This limit is very clearly seen 

 in a specimen treated with acetic acid (Jig- 

 857. b) ; when, as in fig. 858. b t the sec- 

 tion has been transverse, the discs and rods 

 of yellow elastic tissue occupy a position and 

 proportion the reverse of what has been de- 

 scribed. The discs are the most abundant on 

 the outer, and the rods on the inner part of 

 this coat, the former being seen in section, and 

 the latter in profile. 



This middle coat is very compact, especi- 

 ally near the inner surface, and it gradually 

 becomes less so in proceeding outwards. 



It is difficult to tell what is the course and 

 direction of the nidus of white fibrous tissue 

 in which the yellow element is embedded, as 

 in the middle coat it forms a dense granular 

 compact mass*, when seen in situ, and its 

 true nature is only displayed by the action of 

 acetic acid. When, however, portions of the 

 tissue are picked abroad with needles, though 

 its direction is lost, its characters are ob- 

 vious. 



As it regards the muscularity of this coat, 

 there can exist no doubt. Ttie recent ob- 

 servations of Kolliker on the low form of 

 muscle, which he designates " muscular," or 

 "contractile fibre-cells," have placed this pre- 

 viously obscure subject in an intelligible and 

 satisfactory light, and have done much to ex- 

 plode the idea of non-muscular contraction, by 

 exhibiting the wide diffusion of this hitherto 

 unrecognised tissue. 



Kolliker describes two forms of fibre-cells as 

 existing in blood-vessels, one, consisting of 

 short, round, spindle-shaped, or rectangular 

 plates, like epithelium ; the other, of long 

 plates of irregular, rectangular, spindle, or club, 

 shape. The substance of these cells is soft, 

 light yellow, and homogeneous, and each con- 

 tains a peculiar, characteristic nucleus, whose 

 shape is constant, being that of a club or staff. 

 These fibre-cells are placed transversely as it 

 regards the vessel, and constitute a thin coat, 

 immediately external to the lining membrane, 

 intermixed with cellular tissue. These mus- 

 cular elements are clearly seen (as exhibited 

 by their nuclei) by the action of acetic acid 

 on small vessels. (Fig. 860.) 



He further states that the great develop- 

 ment of the uterine veins during pregnancy is 

 principally from an increased size of the fibre- 

 cells existing in the middle coat, but partly 

 also from the inner and outer coat acquiring a 

 considerable quantity of smooth muscular fibre. 

 According to the same authority this mus- 

 cular element is not found in the veins of the 

 uterine portion of the placenta, the cerebral 



* I would here observe, that when white fibrous 

 tissue is dried and re-moistened, as in these sec- 

 tions, it does not regain all its physical characters : 

 it has lost to a great degree its wavy lines, and 

 hence it is not so easily recognized. 



